otherwise, a mod that adds alchemy to the game would be great. Maybe you could add the possibility to combine metals with other items, like blaze powder to make them cause fire damage, or a heart of the sea to give water breathing, or a way to turn iron into gold using experience and vise-versa. I think there's quite a lot that can be done with such a mod, but I don't think it's too complicated, and would fit well into the game.
If you can make flying vehicles, I'd love to see a mod that adds steampunk ships. It's one of the only things I'm missing in terms of mods (besides immersive smithing). Here's a few images for reference that might be good: